Cathode-ray receiver



Feb. 5 1946. wfe. H. FlNCH CATHODE RAY RECEIVER Filed March 25, 1944 2 Sheets-Sheet l FIG. 2'

I INVENTOR.

- W/LLIAMGHJ-INCH 1 BY v ATTORNEY Feb. 5, 1946.

w. G. FlNCH CATHODE RAY RECEIVER Filed March 25, 1944 2 Sheets-Sheet 2 wmT ' INVEN TOR. WILLIAM G. H. FINCH BY ATTORNEY Patented Feb. 5, 1946 UNITED STATES PATENT OFFICE William G. H. Finch, Newtown, Conn.

Application March 25, 1944, Serlal No. 528,065 13 Claims. (01. lie-7,4)

My invention relates in general to the field of picture transmission and reception and more specifically concerns a novel facsimile recorder.

In conventional picture transmission systems, the transmitter may com-prise a rotatable drum supporting the picture to be transmitted.

This drum is helically scanned by an electrooptical system which focuses a sharply defined light spot upon the image. Light reflected from this spot is collected by a photo-electric cell and converted into picture currents which during the rotation of the drum correspond at each instant to the intensity of the picture at that point.

These picture currents are amplified by suitable electronic devices and are transmitted by radio frequency carrier currents or by transmission lines to a remote recorder whereat they are received and amplified for recording.

The recorder comprises essentially a mechanism similar in most respects to the transmitter. Thus a photographic film is supported upon a rotatable drum driven from a suitable source of power.

This film is helically scanned by a light spot in a manner which corresponds to that described for the transmitting-scanning operation and the.

intensity of the light spot is modulated'by the incoming picture signals. It is evident, therefore, that the developed image upon the photographic film will correspond to the image transmitted.

It is, of course, necessary in a picture transmisslon to maintain the rotatable drums at transmitter and recorder in exact synchronism. This problem is solved in many well-known ways and accordingly will not be considered here.

The type of recording light utilized at the re-- ceiver has long been regarded as an important problem. Thus, it is well-known that ordinary filament type bulbs are entirely impractical for facsimile recording, since a filament has a considerable time-lag due to its incandescence, and

such a time-lag in heating and cooling would.

preclude the recording of comparatively high frequency currents.

The principal disadvantage of the discharge type of recording light has been in its comparatively high power consumption for the light energy delivered. This high power consumption has resulted in cumbersome electronic designs for facsimile amplifiers to obtain a current output suflicient to drive this type of recording light at the desired frequency.

Since facsimile receivers may, in many instances, be portable devices where lack of complex amplifier circuits is particularly desirable and where the saving of weight is important, the utilization of gaseous discharge tubes has presented an important disadvantage. In addition, another important disadvantage resulting from the use of gaseous discharge tubes has been that these tubes are designed for extremely specialized purposes and accordingly have been comparatively expensive.

My invention contemplates overcomingall of the disadvantages mentioned for filament type andv gaseous discharge type recording lamps, and proposes to obviate the diillculty of comparatively high expense and high required receiver power output as previously mentioned. Thus, in accordance with my invention, I utilize a conventional radio electron ray tube of the type normally utilized in radio circuits for tuning response indication.

This type of tuning indicator as is well understood in the radio art, comprises essentially a triode mounted in a conventional glass radio tube bulb having a fluorescent target in the dome of the bulb. This target is'operated in such a manner that the electron emission from the cathode causes a glow which covers a sector of the circular area of the target. The extent of this fluorescent glow is determined by the applied grid voltage and of course by the various tube circuit constants.

In normal operation of a tuning eye as in a radio carrier strength detection circuit, it, is conventional to operate the tuning eye grid from a source of voltage within the radio receiver which is proportional or characteristic of the si nal strength received. This voltage is usually obtained from an automatic volume control circuit as is well known, and is highly damped usually by a resistance-capacitance filter.

Thus, the response characteristic of the tuning eye is extremely slow and follows only the very low frequency variations of the signal strength.

position with respect to. a rotatable drum supporting a photographic film at a facsimile recorder. The face of the tuning eye tube is covered by a shield having a small perforation therein. This perforation ordinarily falls within the shadow angle oi the tube when no signal is received.

The facsimile electronic recording circuit is arranged: so that the incoming facsimile signal as detected in a radio frequency circuit or as amplified from an incoming transmission line. is impressed directly upon the control grid of the electron ray tube. No damping means are utilized, and accordingly, the shadow angle of the tube fluctuates rapidly and follows to a. remarkable degree the highest frequency variation of the facsimile signal. This fluctuating shadow angle as viewed through the perforation in the shield of the tuning eye results in a continuous change of illumination of the perforation; and it is this perforation which is focused sharply upon the rotatable drum and its recording film.

Hence, in the manner that the transmitter photo-electric cell receives light fluctuations, the perforation in the shield covering the tuning eye at the receiver is correspondingly illuminated and is focused upon the rotatable receiving drum with the result that the developed photographic image is identical in all respect to the image at the transmitter.

The utilization of an electron ray tube, as Just described. as a facsimile recorder light provides many distant advantages over methods heretofore employed. Inasmuch as an electron tuning eye is a sensitive electronic device for converting signal fluctuations into light fluctuations through the agency of a control grid. the total power requirement of the grid of the tuning eye is extremely small and the receiver electronic amplifiers need only be adjusted to provide sufficient voltage sensitivity-that is, sufilcient voltage amplification from the input to the grid of the electron ray tube to cause the full variation in shadow angle required.

As will be described later in connection with the electron ray tube, this voltage amplification need be comparatively small, and therefore the complexity of the amplifying system is materially reduced. In this manner, the electron ray tube acts as a sensitive light amplifier in that a small grid voltage signal is utilized to control a large amount of light. This controlled light is that which ordinarily is impressed upon the target of the electron ray tube. This system of light control through the grid of an electron ray tube is contrasted against the light control necessary when the picture signals must supply the full energy to alternately illuminate and extinguish a discharge bulb.

It is accordi ly an object of my present invention to provide a novel facsimile recorder.

Another object of my present invention is to utilize an electron ray tube as the source of printing light in an electro-optical facsimile recorder.

A further object of my invention is to utilize the undamped variation of shadow angle of an electron ray tube to photographically record received facsimile signals.

These and other objects of my invention will now become apparent from the following speciflcation taken in connection with the accompanying drawings in which:

Figure 1 is a general view of a facsimile recorder showing the various mechanical features thereof.

Figure 2 is a front view of the electron ray tube shield, and

Figure 3 is a schematic circuit diagram of the novel simplified facsimile recorder.

Referring now to Figure I, there is illustrated a facsimile recorder which may be ut li ed 0 record picture signals received from a distant transmitter.

The recorder illustrated comprises essentially a base plate 2| supporting a drive motor 22 which is rigidh' secured to the base 2|. This motor 22 is the source of power for the entire facsimile unit illustrated and is driven at the some speed as a similar drive motor at a remote transmitter. This may be accomplished by utilizing identical synchronous motors operative from the same power supply or by any of the other well known synchronizing means.

Shaft 24 of the motor 22 drives through coupling It a shaft 2| controlling the gear-ratio box 21. Gear-ratio box drives at a predetermined proper speed, rotatable drum ll rigidly supported upon rotatable shaft 12. Shaft 42 is provided with suitable bearings. one within the gear-ratio box 21 and the other bearing 43 which is bolted at I4 to the base plate 2|.

Also driven from gear-ratio box 21 is a shaft 35 which in turn drives the members of gearratio box 36. A helical feed screw 4| is driven from gear-ratio box 34 and is suitably supported in a hearing within gear-ratio box It and another bearing 42 at the other end thereof. Bearing 42 is secured to the base plate 2| by bolts 43. The rotatable drum 3| supports a photographic film 45 by a mounting bar 44 which is operated by handle 41 in the well known manner.

Removably coupled to helical feed screw 4| is an electro-optical system It incorporating the electron ray tube as will be described. The electro-optical system BI is supported upon helical feed screw 4| by a half-nut l2 pinned at N to the case of the unit II.

In normal operative position, the half-nut 62 engages the helical feed screw 4i and accordingly, rotation of screw 4| will cause lateral displacement of the entire unit 5i.

Upon the completion of a scanning cyc1e-that is, complete lateral movement from one end of the drum to the other. the half-nut 52 is lifted by rotation about pin 53 so that the entire electro-optical unit Il may be restored to its original position.

A shaft BI is rigidly secured to the base plate 2| by fittings 62 at each end thereof. The shaft 6| is smooth and passes through smooth cooperating bearings 63 and 64 fixed to the sides of the electro-optical unit It; and it is evident therefore, that shaft 6| provides additional mechanical support for the system 5 i In accordance with my invention, the electrooptical scanning uit 5i comprises essentially a cast case II having a rear cover plate 12 secured thereto by bolt 13 and a cover 14 secured to the case H by a plurality of bolts 15.

A circular perforation It in the back cover plate 12 ecures a rubber grommet 11 which in turn secures an electron tube adapto 18. The adaptor 18 is Joined by flexible cable 8| to the facsimile recorder electrical circuit as will be described in connection with Figure 3. Plugged into the adaptor T8 is an electron ray tube 82 which is supported in addition by a rubber cushion 83 which has a depression 84 directly molded therein to support the dome of a conventional type tube as illustrated.

The cushion 83 is securely bolted to the case H by a plurality of bolts 85, and accordingly, the electron ray tube 82 is supported in a hock-proof manner which in addition facilitates removal and repair. The cushion ll isperforated at Si in order not to obstruct the dome of the tube 42.

accuse A metal plate 92 is, as illustrated, secured to the case II of the electro-optical system between the rubber cushion I3 and the front wall .of the case. A perforation 93 within the metal plate 92 functions in a manner which will be described in connection with Figure 2.

A circular tapp d perforation 95 in the front of the case II i in a position coaxial with the electron ray tube 82 and supports an optical unit 95. Thus, the optical unit 95 comprises essentially a metal tube 91 having a shoulder 99 and a threaded extension which engages the thread in the hole 95, to form a rigid mounting as illustrated.

Within the metal tube 91 are securely cemented lens elements I92 which function in a manner to be described in greater detail later. Thus, the electro-optical system 5I due to its simplicity of mechanical construction may be readily disassembled for repair and fo adjustment as required during service.

Referring now to Figure 2, the operation of the electron ray tube will be described in greater detail. Thus the metal plate 92 covers as illustrated the dome 92 of the electron ray tube 92. The perforation 93 in the metal plate 92 is formed between the radial lines III and I I2, and the circular line II 3 and III which are concentric with the center H5 the electron ray tube 92. The center II normally corresponds to the cathode of this tube.

when the electron ray tube 82 is in operation as in a circuit of the type to be described in connection with Figure 3. a shadow area I I5 is formed upon the target of the electron ray tube between a large illuminated area II 5 of the same target. This fluorescent area as is well known for electron ray tubes covers the entire circumferential area between the lines III and III! which represent theboundaries of the shadow area II5.

Ordinarily, for' a tuning eye tube such as the 6E5 or other types, the shadow area II5 for zero signal input is approximately 90 and the fluorescent area IIG approximately 270 of the surface v of the target. The fluorescent area I I8 is bounded on the inside by a circle I2I representing the oathode shield and other circuit elements within the tube and on the outside by a circle I22 representing the outer edge of the target and which in turn is essentially the edge of the dome 82' of the electron ray tube. I

As utilized in my novel facsimile recorder, the perforation 93 is arranged to cover the shadow area, when no signal is received, between the edge Hit of the fluorescent area IIS and the center line I23 of the shadow area illustrated.

Accordingly as viewed from the front of the electro-optical scanning system SI of Figur 1, the metallic shield 92 will show a dark area of the shape of perforation 93 illustrated in Figure 2,

under the condition of zero signal input. As the signal input increases, the fluorescent area I I6 lustrated in Figure 1, the gear-ratio boxes 21 and 35 are so adjusted in connection with drivin motor 22 that the rotatable drum 3I rotates at a suitable speed and that the lateral displacement of electro-optical unit 5I is such to cause the spot I3I to trace a continuous helical line about the surface thereof. If during this scanning operation, the incoming signal is applledto electron raytube 92 to cause a fluctuation in shadow angle or a fluctuation of illuminated area over the area of perforation 93, the spot I3I will will increase and accordingly boundaries III and I I8 of the shadow area I I5 will'converge upon the center line I23 which line represents the condition of a signal input large enough to cause the edges I I1 and I I8 to merge.

For any condition, therefore, of signal input between the extremes of zero signal input indicated by the position of lines II! and H8 of Figure 2, and the iii-.aximum signal input which causes the convergence of edges III and H8 at line I23, the perforation 93 will be illuminated by a portion of fluorescent area I I6, and at all times this illu mination of perforation 93 will be directly pro portlonal to the strength of the incoming signal record the incoming picture signal directly upon the surface of film 45.

In order to now illustrate how the utilization of the electron ray tube for photographic recording at a facsimile receiver simplifies the construction of the electronic circuit of a facsimile recorder, reference is made to Figure 3.

If the facsimile signals are transmitted in the form of a modulated carrier, then, as illustrated in Figure 3, these signals are received by antenna I5I which through tuned circuit I52 are im pressed upon a radio frequency amplification circuit I53.

As is conventional, the output of the radio frequency unit I53 and the output of a local oscillator I54 are impressed upon a conversion circuit to produce an intermediate frequency within the circuit I55. After suitable intermediate frequency amplification within the intermediate frequency stages I55, these received signals are demodulated within detector I56 and are then suitably amplified to operate the facsimile printing circuit.

Previously, it has been necessary to resort to considerable voltage amplification in order to operate a power amplifier which would in turn control the light fluctuations of a discharge type tube.

In accordance with my invention, since an electron ray tube such as 82 has comparatively great sensitivity, in that a small fluctuation of grid voltage can control a considerable light intensity as demonstrated in Figures 1 and 2, the output of detector I56 may if desired be utilized directly to operate the electron ray tube 92, or as illustrated in Figure 3, may operate a conventional type of voltage amplifier I5'I. Thus, the output of detector I56 is applied through resistor I58 to the control grid of vacuum tube I6I. The cathode of this tube I6I is grounded through self-biasing resistor I52 and by-pass condenser I63 as is conventional.

The suppressor grid is internally connected to the cathode and the screen grid is connected to a source of highvoitage direct current I65 through resistor I66. A by-pass condenser I61 connects the screen grid to ground.

The plate of vacuum tube I6I is also connected to the high voltage direct current source I65 through load resistor III and the output at the plate of vacuum tube I6I is coupled by coupling condenser I12 and grid resistor I13 directly to the control grid of electron ray tube 82. The electron ray tube 82 comprises as is well known in the art a cathode I" which as illustrated is connected through a' variable resistor IIIS to ground. A by-pass condenser H8 is utilized in connection with resistor I to obtain the desired cathode bias to operate the shadow angle of the tube such that it is a maximum at the zero input to the control grid across resistor In and is zero angle when the maximum incoming signal is applied to this grid.

The plate I11 and the target I'I8 are interconnected within the tube and are maintained at a positive potential by a connection to the direct current source I65 through a load resistor I8I.

A ray control electrode I82 is directly connected to the voltage source I85.

With the cathode bias properly adjusted by variable resistor I15, the extent of the shadow area IIS as illustrated in Figure 2 is directly controlled, with practically no power whatsoever, by the control grid IIII is sufiiclent to cause the variation from black in the perforation 83 to full illumination over this area. Since this perforation is comparatively large before being focused down to the spot I3I upon the rotatable drum 8|, the amount of light controllable by the grid I10 is comparatively great.

As the incoming signal increases, it is evident in Figure 3 that the plate current of tube 82 will increase, and accordingly, the potential of the plates I11 and the target I18 will decrease when compared with the ray control electrode I82. It is this variation between target voltage and ray control voltage, which as is well known, controls the extent of the shadow angle of the tube 82. The connections to tube 82 as illustrated by flexible connector 8I in Figure 1, need be only those connections required for tube 82 as illustrated in Figure 3.

For the 6E5 electron ray tube such as illustrated by 82 in the figures, the shadow angle varies substantially linearly with the grid voltage. Thus for a plate voltage of 250 volts the shadow angle varies through 90 for a variation of grid voltage of 8 volts.

As the plate and target voltage of the control tube 82 are lowered, the sensitivity shadow angle variation is increased. Thus, if the target and plate voltage is lowered to 100 volts 9. variation of 3 volts on the grid IIII of the tube 82 will cause the complete variation from zero to 90 of shadow angle as required to reproduce the complete range of black to white in the focused spot Of course, the reduction of the plate and I3I. target voltage may effect the intensity of the light spot I3I, and therefore, this increase in the sensitivity is accomplished only through a sacrifice in printing sensitivity. However, for extremely sensitive film and for comparatively slow speed recording, this is not a serious objection.

The focused light spot I3I upon the film 45 may, if extremely sharply defined, be an area identical to perforation 93 in the disk 92. It is evident from the consideration of Figure 2, that, as the perforation 93 is positioned, the increase in grid voltage will cause only one side of the perforation to become illuminated; and accordingly, it may result in a focused spot I 3| which varies in intensity and in width with the variation in picture signal intensity. However, if the optical system is such as to produce a slightly defocused spot I3 I, this variation in illuminated area of the spot will cease to be noticeable.

It is evident from Figure 2 that a diflerent modification of printing perforation 83 may be utilized. Thus, the center of perforation 83 may be disposed directly on the center line I23 of the shadow area, and the tube may be initially biased to produce a shadow angle which corresponds to the angular distance covered by perforation 83. Accordingly, an increase in signal strength would cause both edges III and H8 of the fluorescent area IIB to close over the radial edges of perforation 93; and accordingly, if a sharply defined printing spot were focused upon photographic film 45, the spot would consist of a dark center line bordered on each side by a bright line representing the over-lapping area covered by the fluorescent area H8 in the perforation 83. Again, if the spot I 3| is de-focused, this effect will not in any way hinder faithful reproduction.

As is well known, if the intensity of the received signals is raised, the lines III and H8 bordering the fluorescent area of Figure 2 will converge and if it is increased still further, will overlap to produce a brighter line at the overlapping area. This effect is not particularly desirable if linearity of recording is to be obtained; and accordingly, it is necessary to adjust the bias of the tube 82 so that the incoming signals will not rise to a maximum to cause such overlapping.

It is also evident in Figure 2 that the particular shape illustrated for perforation 88 was chosen such that the linearity between signals input and light variation over the perforation 88 is obtained.

It is therefore evident that my invention provides means for electronically controlling a considerable amount of light which may be utilized for photographic facsimile recording.

Since these are many modifications of electron ray tubes and many modifications of the circuits in which they may be incorporated, I wish that the electron ray facsimile recording disclosure above be limited not by the specification and drawings, but by the appended claims.

I claim:

1. In a facsimile recorder, means for receiving picture signals and means for recording said picture signals comprising an electron ray tube having a luminous sector fluctuating in accordance with said picture signals from a complete circle to a predetermined sector, and a shield positioned between said electron ray tube and a photographic film covering the variable luminous sector and having an opening therein for exposing the luminous sector adjacent thereto.

2. In a facsimile recorder, means for receiving picture signals and means for recording said picture signals comprising anelectron ray tube having a luminous sector fluctuating in accordance with said picture signals, said electron ray tube being operative from a comparatively low power picture signal voltage amplifier, and a shield positioned between said electron .ray tube and a photographic film covering the variable luminous sector and having an opening therein for exposing the luminous sector adjacent thereto.

3. In a facsimile recorder, means for receiving picture signals, means for scanning a light sensitive film, said scanning means including an electron ray tube having a fluorescent screen, means for illuminating a variable sector of said fluorescent screen, and a shield adjacent the position of said screen which is variably illuminated and having an opening therein forexposing the adjacent portion of the screen, and means for sharply focussing said exposed area of said fluorescent screen upon said film.

4. In a facsimile recorder, means for receiving picture signals, means for scanning a light sensitive film, said scanning means-including an electron ray tube having a fluorescent screen, a shield between said electron ray tube and said film, a perforation in said shield, said perforation normally covering the shadow angle of said electron ray tube.

5. In afacsimile recorder, means for receiving picture signals, means for scanning a light sensitive film, said scanning means including an electron ray tube having a fluorescent screen, a shield between said electron ray tube and said fllm, a perforation in said shield, said perforation normally covering the shadow angle of said electron ray tube, and means for focussing said perforation upon said film.

6. An electron ray tube having a fluorescent target, means for applying a control voltage to said tube to cause a substantial sector of said target to glow, means for light shielding said target to normally render the glowing sector of said tube invisible, said shielding means having an opening therein arranged so that when the glowing sector extends beyond a predetermined limit the glow from said target is visible.

7. An electron ray tube having a fluorescent target,'means for applying a control voltage to said tube to cause a substantial sector or said target to glow, means for light shielding said target to normally render the glowing sector of said tube invisible, said shielding means having an opening therein arranged so that when the glowing sector extends beyond a predetermined limit under control or said control voltage, the glow from said target is visible.

8. An electron ray tube having a fluorescent target varying in accordance with received signals, means for applying a control voltage to said tube to cause a substantial sector or said target to glow, means for light shielding said target to normally render the glowing sector of said tube invisible, said shielding means having an opening therein arranged so that when the glowing sector extends beyond a predetermined limit under control oi said control voltage, the glow from said target is visible.

9. An electron ray tube having a fluorescent target varying in accordance with received picture signals. means for applying a control voltage to said tube to cause a substantial sector said target to glow, means tor light shielding said target to normally render the glowing sector of said tube invisible, said shielding means having an opening therein arranged so that when the glowing sector extends beyond a predetermined limit under control of said control voltage, the glow from said target is visible.

v 10. An electron ray tube having a fluorescent target varying in accordance with received picture signals, means for applying a control voltage to said tube to cause a substantial sector of said target to glow, means for light shielding said target to normally render the glowing sector of said tube invisible, said shielding means having an opening therein arranged so that when the glowing sector extends beyond a predetermined limit under control of said control voltage, the glow from said target is visible, and means for focusing the visible portions of said luminous target.

11. An electron ray tube having a fluorescent member, means for causing a variable sector of said fluorescent member to be luminous, a shield covering the luminous sector, an opening in the shield exposing only a portion 01 the sector where the luminous ends meet when saidmeans extends the luminous sector beyond a predetermined value.

12. An electron ray tube having a fluorescent member, means for causing a variable sector oi said fluorescent member to be luminous, a shield covering the luminous sector, a slot' in the shield exposing only a portion of the sector which is normally not luminous, said means operating in response to received signals to extend'the luminous sector into the portion exposed by said slot.

13. In a signalling system, a radio receiver including a radio frequency receiving circuit. a radio frequency detector and an electron ray tube having a control grid, means including circuit connections directly from said detector to said control grid, said electron tube having a fluorescent member, means whereby said control grid causes a sector of said fluorescent member to be luminous, a slot in the shield exposing only a portion of the sector which. is normally not luminous, said means operating in response to received signals to extend the luminous sector into the portion exposed by said slot.

1 WILLIAM G. H. FINCH. 

